Conventionally, there has been proposed a device in which an exhaust flow divider is provided in an exhaust path, the exhaust flow divider causes an exhaust to flow an EGR gas with PM unevenly distributed and a remaining discharged gas in a divided manner, the EGR gas is recirculated to a combustion chamber, and the discharged gas is discharged to an atmospheric side (see, for example, Patent Document 1).
According to an exhaust treatment device for a diesel engine of this type, the PM contained in the EGR gas is incinerated by heat generated from incineration in the combustion chamber during an engine operation. As a result, a DPF can be omitted. Alternatively, the DPF can be miniaturized by using the DPF and the exhaust flow divider in combination. In other words, since it is not necessary to store much PM, the exhaust flow divider can be more miniaturized than the DPF. In both a case where the exhaust flow divider is used instead of the DPF and a case where the DPF and the exhaust flow divider are used in combination, there is an advantage that the engine can be miniaturized.
However, since an NOx reduction treatment of the discharged gas is not performed, this conventional technology is problematic.